doc: repeat a remark as needed in the buffer.md

PR-URL: https://github.com/nodejs/node/pull/9795
Reviewed-By: Sam Roberts <vieuxtech@gmail.com>
Reviewed-By: Roman Reiss <me@silverwind.io>
Reviewed-By: Anna Henningsen <anna@addaleax.net>

doc/api/buffer.md

@@ -2306,6 +2306,9 @@ added: v3.0.0
 On 32-bit architectures, this value is `(2^30)-1` (~1GB).
 On 64-bit architectures, this value is `(2^31)-1` (~2GB).
 
+Note that this is a property on the `buffer` module as returned by
+`require('buffer')`, not on the `Buffer` global or a `Buffer` instance.
+
 ## buffer.transcode(source, fromEnc, toEnc)
 <!-- YAML
 added: v7.1.0
@@ -2333,6 +2336,9 @@ console.log(newBuf.toString('ascii'));
 Because the Euro (`€`) sign is not representable in US-ASCII, it is replaced
 with `?` in the transcoded `Buffer`.
 
+Note that this is a property on the `buffer` module as returned by
+`require('buffer')`, not on the `Buffer` global or a `Buffer` instance.
+
 ## Class: SlowBuffer
 <!-- YAML
 deprecated: v6.0.0